Question

(b) What intensity level of the horn's sound is dB him and 476 Hz when the train is receding from him. Using these frequendies, he calculates the speed of the train. What value does he find? (Assume the speed of sound in air is 343 89

Answer 1

4)
First find the intensity of a 56dB sound using β = 10dB*log(I/10^-12)

so I = 10^(56/10)*10^-12= 3.981*10^-7 W/m²

Now P = I*A = 3.981*10^-7*4π*(10000m)² = 500.26 W

b) at 46m the intensity = P/A = 500.26W/(4π*46²) = 0.01881 W/m2

This corresponds to a level of 10dB*log(0.01881/10^-12) = 102.74dB

5)

$\frac{487}{476}=\frac{345+v_{t}}{345-v_{t}}$

(487 - 476) / (487 +476) ={ 345 + v - (345 - v) } / {345 + v + 345 - v}

11/ 963 = 2v / 2(345)
11/ 963 = v / 345
v_t = 3.94 m/s